ISO Sensitivity / Noise levels (JPEG)

Standard Test

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor to enable faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" (gain) on the CCD's signal amplifiers. Nothing is without its price however and doing so also typically increases visible noise (random speckles visible all over the image).

We are now using a more reliable, repeatable and neutral method for evaluating noise. Shots are taken in daylight lighting in our studio. Noise is measured as the standard deviation of the medium gray patch on a Gretag MacBeth ColorChecker chart. The image is normalized before measurement of noise to remove the possibility of figures being affected by images with low contrast. Note that noise numbers shown on the graphs below can not be compared to those in older reviews.

In the comparisons below we used aperture priority mode and selected an aperture which would produce a shutter speed as near as possible the selected sensitivity value (ie. ISO 200, 1/200 sec).

Test notes:

• Shots taken at approximately 21°C (~70°F)
• Lighting was simulated daylight measured as 10.1 EV (at ISO 100)

Kodak DCS Pro SLR/c vs. Canon EOS-1Ds JPEG (ISO 100 - 1250)

• Kodak DCS Pro SLR/c: Canon 50 mm F1.4 lens, Aperture Priority (F3.5), Manual WB,
  Default Parameters, 50 mm F1.4, JPEG Large / Fine
  
• Canon EOS-1Ds: Canon 50 mm F1.4 lens, Aperture Priority (F4), Manual WB,
  Default Parameters, 50 mm F1.4, JPEG Large / Fine

	Kodak DCS Pro SLR/c n/a	Canon EOS-1Ds ISO 100, 1/100 sec, F4
Partial crop
Red Green Blue channels
	Kodak DCS Pro SLR/c ISO 160, 1/160 sec, F3.5	Canon EOS-1Ds (ISO 160 not shot)
Partial crop
Red Green Blue channels
	Kodak DCS Pro SLR/c ISO 200, 1/200 sec, F3.5	Canon EOS-1Ds ISO 200, 1/200 sec, F4
Partial crop
Red Green Blue channels
	Kodak DCS Pro SLR/c ISO 400, 1/400 sec, F3.5	Canon EOS-1Ds ISO 400, 1/400 sec, F4
Partial crop
Red Green Blue channels
	Kodak DCS Pro SLR/c ISO 800, 1/800 sec, F3.5	Canon EOS-1Ds ISO 800, 1/800 sec, F4
Partial crop
Red Green Blue channels
	Kodak DCS Pro SLR/c n/a	Canon EOS-1Ds ISO 1250, 1/1250 sec, F4
Partial crop
Red Green Blue channels

Thanks to the SLR/c's built-in (and impossible to disable) noise reduction algorithm it manages to keep noise levels consistently lower than the EOS-1Ds up to ISO 400, as you can see from the luminance noise graph below there is a significant jump in noise at ISO 800. Increasing noise reduction to the 'Strong' level helps to reign it in, although as we have seen on previous pages Kodak's heavy handed noise reduction algorithm has a significant detrimental effect on the image leaving it with blotchy watercolor like artifacts.

Luminance noise graph (ISO 100 - 1600)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity (normalized) on the vertical axis.

RGB noise graph (ISO 100 - 1600)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized) are on the vertical axis. Note that measurements were not made at every ISO sensitivity.